Synthetic thickeners for cosmetics

ABSTRACT

Disclosed are inverse emulsions for the preparation of cosmetic formulations wherein the weight ratio between the aqueous phase and the organic phase is from 4:1 and 2:1 and containing Ron 20 to 70% buy weight of an acrylic polymer obtained by inverse emulsion polymerisation of from 55 to 75% by weight of an anionic acrylic monomer containing a strongly acidic functional group; Ron 0.1 to 5% by weight of a cationic acrylic monomer if the formula (I). Wherein R 1  is hydrogen or methyl; R 2 , R 3 , R 4  are, one independently of the others, hydrogen or C 1 -C 4  alkyl; Y is NH or O; A is a C 1 -C 6  alkylene; from 25 to 45% by weight of a C 3 -C 5  anionic acrylic monomer containing a carboxylic group. Also disclosed is the procedure for their preparation.

The present invention relates to inverse emulsions useful as thickenerin cosmetic formulations and to the procedure for their preparation.

Particularly the inverse emulsions of the invention comprise a polymerobtained by polymerisation of two or more acrylic anionic monomers, atleast one of which containing a strong acid functionality (and morespecifically a sulfonic functional group), and of at least one monomercontaining cationic groups.

The inverse emulsions of the invention possess high skin and haircompatibility, which makes them particularly suited for the preparationof cosmetic formulations, and exhibit good thickening properties andstability over time.

With the expression “cosmetic formulations” we mean the productsnormally used for personal care, such as body and face creams, hair gelsand lotions, hair colouring and bleaching creams, sunscreencompositions, make-up products, cleansing, moisturizing and perspiringfluids and other products for similar applications.

It is known that a technical problem often encountered in the cosmeticindustry is to obtain high viscous formulations (pastes, gels) stableover time and exhibiting high compatibility with skin and hair.

An essential characteristic of the thickeners employed in cosmeticformulations is that they manifest their thickening capability withoutnegatively altering the other properties of the formulations.

In the specialised literature many methods are reported to regulate therheological properties of different formulations, often including theuse of polymers in the form of inverse emulsion (an inverse emulsion isan emulsion containing both an oil-in-water emulsifier and awater-in-oil emulsifier, wherein the aqueous phase is dispersed in theorganic phase in very small drops), but the synthetic thickeners forcosmetics of the present invention are never described.

We cite as an example:

-   -   EP 503853, wherein an inverse emulsion containing a polymer        comprising units deriving from acrylamide,        2-acrylamido-2-methylpropanesulfonic acid and a polyfunctional        monomer is described; a disadvantage of the inverse emulsions of        EP 503853 is the fact that they contain traces of acrylamide, a        toxic substance which is unacceptable by the present European        legislative trend;    -   U.S. Pat. No. 6,375,959 and U.S. Pat. No. 6,197,287 wherein a        procedure for the preparation of cross-linked or branched        polyelectrolytes based on strongly acidic monomers and other        monomers, but not acrylamide, in the form of an inverse        emulsion, is described;    -   U.S. Pat. No. 6,329,483, wherein copolymers of carboxylic acids        and quaternary ammonium compounds and the preparation of gels        and emulsions containing the same is described;    -   US 2001/0023284, wherein copolymers of a neutral monomer        (N-alkylacrylamide) with one or more monomers selected among        cationic monomers, monomers bearing strongly acidic functional        groups and monomers bearing weakly acidic functional groups are        described.

It is still desirable in the cosmetic field to have thickeners in theform of stable emulsion that are able to give stable cosmeticformulations, and that, in addition to a good thickening efficiency indifferent conditions and ease of use, exhibit an improved compatibilitywith skin and hairs. With the expression “stable emulsion” we mean anemulsion that in the normal storing conditions (from −10° C. to 40° C.)and for the usual lifetime (180-360 days) does not show phaseseparation, sediment, formation of floating pellicles and lumps.

With the expression “stable cosmetic product” we mean a cosmeticformulation that in the above said conditions and lifetime does not showphase separation, sediment, formation of floating pellicles and lumps.

By cosmetic product with high compatibility with skin and hair we mean aproduct that is easily absorbed through a keratinous substrate whilemaking changes in the touch, in moisturisation and perspiration, andimproving the general sensorial characteristics without altering thephysiological pH.

It has now surprisingly been found that the inverse emulsions containingan acrylic polymer obtained by inverse emulsion polymerisation of ananionic acrylic monomer containing a weakly acidic functional group, ananionic acrylic monomer containing a strongly acidic functional groupand an acrylic cationic monomer of the formula (I)

wherein

R₁ is hydrogen or methyl;

R₂, R₃, R₄ are, one independently of the others, hydrogen or C₁-C₄alkyl;

Y is NH or O;

A is a C₁-C₆ alkylene; X is chloride,

possess a stability which is perfectly suited for their industrial usein cosmetic formulations, even many months after their preparation;furthermore the inverse emulsions of the Invention enable thepreparation of cosmetic formulations with very good compatibility withskin and hair. It is well known that the combined presence of twodifferent functionalities in the same macromolecule, a cationic one andan anionic one, tends to be the cause of coagulation; coagulation canoccur both in the phase preceding the reaction (when monomers havingopposed functionality are mixed together), and while the reaction takesplace, during the polymer formation.

An insufficient distribution of the charges in the macromolecule itselfincreases its solubility in the oily phase and leads to its desorptionfrom the water phase where the reaction takes place,

The polymer desorption and its consequent dissolution in the oily phaseusually causes the coagulation of the dispersed system and gelation.

It has surprisingly been observed that coagulation and gelation can beprevented by operating within the limits of the present invention.

It is a fundamental object of the present invention an inverse emulsionfor the preparation of cosmetic formulations wherein the weight ratiobetween the aqueous phase and the organic phase is from 4:1 to 2:1 andcontaining from 20 to 70% by weight of an acrylic polymer obtained byinverse emulsion polymerisation of

-   -   i. from 55 to 75% by weight, and preferably from 60 to 70% by        weight, of an anionic acrylic monomer containing a strongly        acidic functional group;    -   ii. from 0.1 to 5% by weight, and preferably from 2 to 4% by        weight, of a cationic acrylic monomer of the formula (I)        -   wherein        -   R₁ is hydrogen or methyl;        -   R₂, R₃, R₄ are, one independently of the others, hydrogen or            C₁-C₄ alkyl;        -   Y is NH or O;        -   A is a C₁-C₆ alkylene; X is chloride,    -   iii. from 25 to 46% by weight, and preferably from 30 to 40% by        weight, of a C₃-C₅ anionic acrylic monomer containing a        carboxylic group.

The anionic acrylic monomer containing a strongly acidic functionalgroup is selected among the monomer of this kind that are normallyemployed for the preparation of polymeric synthetic thickeners for thecosmetic use; among those, 2-acrylamido-2-methylpropanesulfonic acid isparticularly suited for the realisation of the present invention.

Preferably the cationic acrylic monomer of the formula (I) is selectedfrom acryloyloxyethyl-trimethylammonium chloride andmethacryloyloxyethyl-trimethylammonium chloride and the C₃-C₅ anionicacrylic monomer containing a carboxylic group is selected from acrylicacid and methacrylic acid.

According to a fundamental aspect of the invention the acrylic polymerobtained by inverse emulsion polymerisation is cross-linked with from0.01 to % by weight of a compound containing two or more ethylenicgroups, preferably with methylene-bis-acrylamide.

It is a further object of the present invention a procedure for thepreparation of an inverse emulsion for cosmetic formulationscharacterised by:

-   -   a. preparing a composition consisting of from 40 to 60% by        weight of water, and for the remaining percentage by weight of a        mixture of acrylic monomers consisting of:    -   i. from 55 to 75% by weight, and preferably from 60 to 70% by        weight, of an anionic acrylic monomer containing a strongly        acidic functional group;    -   ii. from 0.1 to 5% by weight, and preferably from 2 to 4% by        weight, of a cationic acrylic monomer of the formula (I)        -   wherein        -   R₁ is hydrogen or methyl;        -   R₂, R₃, R₄ are, one independently of the others, hydrogen or            C₁-C₄ alkyl;        -   Y is NH or O;        -   A is a C₁-C₈ alkylene; X is chloride,    -   iii. from 25 to 45% by weight, and preferably from 30 to 40% by        weight, of a C₃-C₅ anionic acrylic monomer containing a        carboxylic group;    -   b. adding to the composition prepared in a. an aqueous solution        of an alkali to regulate the pH between 4 and 7, a cross-linking        agent and an initiator of radical polymerisation, maintaining        the temperature between 3 and 7° C.;    -   c. preparing an organic phase containing one or more        water-in-oil emulsifiers;    -   d. introducing the mixture obtained in be into the organic phase        prepared in c. and emulsifying the two phases by vigorous        stirring;    -   e. initiating the polymerisation and completing it maintaining        the temperature between 55 and 95° C. under vigorous stirring;    -   f. cooling the reaction mixture to 35-45° C. and adding an        oil-in-water emulsifier.

As it was previously said about the inverse emulsion of the invention,the anionic acrylic monomer containing a strongly acidic functionalgroup is selected among the monomers that are normally employed for thepreparation of polymeric synthetic thickeners for the cosmetic use;among those, 2-acrylamido-2-methylpropanesulfonic acid is particularlysuited for the realization of the present invention,

Preferably the cationic acrylic monomer of the formula (I) is selectedfrom acryloyloxyethyl-trimethylammonium chloride andmethacryloyloxyethyl-trimethylammonium chloride and the C₃-C₅ anionicacrylic monomer containing a carboxylic group is selected from acrylicacid and methacrylic acid.

In the procedure of the invention, normally, the alkali used is NaOH.

According to another aspect of the invention, the acrylic polymerobtained by inverse emulsion polymerisation is cross-linked with from0.01 to 1% by weight of a compound containing two or more ethylenicgroups, preferably with methylene-bis-acrylamide.

Among the initiators of radical polymerisation utilisable for therealisation of the present invention are ammonium, potassium or sodiumpersulfate, and water-soluble organic peroxides, by way of examplehydrogen peroxide and peracetic acid.

In the inverse emulsions of the invention the organic phase consists ofby mineral oils containing saturated hydrocarbons or by vegetable oilsor by mixture thereof having boiling point from 150 to 300° C.

Preferably the organic phase is a C₁₃-C₁₆ iso-paraffin.

The water-in-oil and the oil-in-water emulsifiers are those normallyused for this purpose.

We cite among the utilisable water-in-oil emulsifiers: sorbitanmonolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitanmonooleate; among the utilisable oil-in-water emulsifiers we cite thelinear or branched ethoxylated alcohols.

To initiate the polymerisation of the acrylic monomers advantageously anaqueous solution of sodium metabisulfite is used.

The inverse emulsions of the invention may further additionally containthe common additives used in radical polymerisation, by way of examplesequestering agents such as sodium diethylenetriaminepentaacetate.

As it was previously observed, the inverse emulsions of the presentinvention are particularly suited for the treatment of hair and skin, inbody and face creams, hair gels and lotions, hair colouring andbleaching creams, sunscreen compositions, make-up products, cleansing,moisturizing and perspiring fluids.

In the following examples the preparation of inverse emulsions accordingto the invention and of some cosmetic formulations containing them isreported.

The following examples illustrate the present invention without limitingit, nor the kind of application of the inverse emulsions of theinvention.

EXAMPLE 1

The following ingredients are loaded into a 1.5 l pirex reactor equippedwith a steel anchor stirrer:

62.21 g deionised water;

573 g aqueous solution (50% by weight) of sodium2-acrylamido-2-methylpropane sulfonate;

135 g acrylic acid;

15.8 g ADAMQUAT MC 80 (acryloyloxyethyl-trimethyl ammonium chloride soldby Atofina).

After a cooling down period, necessary to reach a temperature close to0° C., the following ingredient are slowly added while stirring:

112.38 g aqueous solution (50% by weight) of NaOH;

10 g aqueous solution (1% by weight) of methylene-bisacrylamide;

0.5 g aqueous solution (40% by weight) of sodiumdiethylenetriaminepentaacetate;

10.75 g aqueous solution (4% by weight) of ammonium persulfate. In themeantime, the organic phase is prepared inside a 500 ml beaker addingunder stirring:

20 g sorbitan monooleate;

214.8 g C₁₃-C₁₆ hydrocarbon isoparaffin.

The aqueous phase is slowly added into the organic phase andsubsequently the mixture is efficiently stirred with a high sheardispersing machine (ultra-turrax IKA).

The emulsion obtained is then reloaded in the reactor and the reactionis ready to be started (reaction phase). The first operation is toinsufflate nitrogen directly in the bulk of the product for about 10minutes. This is a key step, because it enables to lower and control theamount of oxygen dissolved in the emulsion and to adjust the inductiontimes. The second phase takes place only after the emulsion temperatureis warmed up to 20° C. After that, 21.5 g of a 1% by weight aqueoussolution of sodium metabisulfite is quickly loaded drop-wise through anaddition funnel. The third phase is the radical reaction. The reactionproceeds spontaneously raising gradually the temperature to about 60° C.in 50 minutes. The stirring is maintained very fast and cool waterre-circulates inside the reactor jacket. After this period of time theemulsion is kept at 60° C. for about one hour to complete the monomersconversion, consuming the residual monomers. Subsequently a cooling downperiod is required to reach a temperature of 35-40° C. The final step isthe addition of 25 g of C₁₂-C₁₆ (8 moles) ethoxylated linear alcohol.

The mixture is rapidly stirred till homogeneity is reached; the finalemulsion (Emulsion 1) is then unloaded and stored for at least 24 hoursbefore the evaluation of its properties.

Property evaluation of Emulsion 1.

Samples of Emulsion 1 are stored at different temperatures.

The emulsion stability is evaluated at different temperatures byvisually checking possible phase separation or settling on the bottom ofthe vessel using a glass stick.

In the following table (Table 1) the test temperatures and minimalstability times of the emulsion are shown. TABLE 1 Temperature −3° C.20° C. 45° C. Stability >30 >100 >30 (days)

The thickening properties are instead evaluated as follows and are shownin Tables 2 and 3.

A 2% by weight aqueous solution of Emulsion 1 is prepared in deionizedwater with high stirring in a 1 litre beaker.

Subsequently the viscosity is measured at 20° C., at different pH values(see Table 2) and adding different concentration of electrolyte (NaCl,as shown in Table 3).

The pH was adjusted by additions of an aqueous solution (50%) of citricacid. TABLE 2 Brookfield Viscosity in mPa · s (spindle 6, after 24 h) 5rpm 10 rpm pH 70000 41000 6.8 13200 8200 6.6 3200 2100 5.2 400 300 4.2rpm = rounds per minute

TABLE 3 Brookfield Viscosity in mPa · s (spindle 6, after 24 h, pH =7.5) 0.01% 0% NaCl NaCl 0.02% NaCl 0.03% NaCl 0.04% NaCl  5 rpm 7000052200 38000 26400 18800 10 rpm 41000 30000 22000 16000 11500rpm = rounds per minute

EXAMPLE 2

An inverse emulsion is prepared as described in Example 1, substitutingADAMQUAT MC 80 in the aqueous phase with 16.9 g of MADQUAT MC 75(methacryloyloxyethyl-trimethyl ammonium chloride, 75% by weight inwater, sold by Atofina) thus obtaining Emulsion 2.

Property evaluation of Emulsion 2.

Samples of Emulsion 2 are stored at different temperatures.

The emulsion stability is evaluated at different temperatures byvisually checking possible phase separation or settling on the bottom ofthe vessel using a glass stick.

In the following table (Table 4) the test temperatures and minimalstability times of the emulsion are shown. TABLE 4 Temperature −3° C.20° C. 45° C. Stability >30 >100 >30 (days)

The thickening properties are evaluated as described for Emulsion 1 andare shown in Tables 5 and 6. TABLE 5 Brookfield Viscosity in mPa · s(spindle 6, after 24 h) 5 rpm 10 rpm pH 77000 45600 7.1 61800 36600 6.930000 17500 6.4 17800 10700 6.1 7000 4500 5.6 800 600 4.7rpm = rounds per minute

TABLE 6 Brookfield Viscosity in mPa · s (spindle 6, after 24 h, pH =7.5) 0.01% 0% NaCl NaCl 0.02% NaCl 0.03% NaCl 0.04% NaCl  5 rpm 7700064000 49600 39000 27800 10 rpm 45600 38000 29400 23100 16200rpm = rounds per minute

EXAMPLE 3

A body cream is prepared using Emulsion 1; all the ingredients arelisted in Table 7 and the procedure is described in the followingparagraph. TABLE 7 Body cream. Ingredients % Phase A Aqua to 100Glycerin 3 EDTA 0.1 Emulsion 1 0.4 Phase B Hydrogenated Polydecene 15Prunus Amygdalus dulcis 5 Caprylic/capric triglyceride 4 Steareth-2 2Steareth-21 3 Phase C Preservative 1 Phase D Parfum 0.1

Phase A is prepared by homogenising all the ingredients at roomtemperature and then heating the mixture to 70° C.

Phase B is prepared heating all the ingredients to 70-75° C.; Phase A isadded to Phase B stirring vigorously. The mixture is cooled down to 40°C. and Phase C and Phase D are added, stirring till homogeneity isreached.

Properties of the cream obtained:

Viscosity=31000 mPa.s (5 rpm, spindle 4); 44500 mPa.s (2.5. rpm spindle4)

pH=7.3

EXAMPLE 4

A foundation is prepared using Emulsion 2; all the ingredients arelisted in Table 8 and the procedure is described in the followingparagraph. TABLE 8 Foundation. Ingredients % Phase A Aqua to 100Glycerin 3 EDTA 0.1 Emulsion 2 0.4 Phase B Hydrogenated Polydecene 15Prunus Amygdalus dulcis 5 Caprylic/capric triglyceride 4 Steareth-2 2Steareth-21 3 Unipure Brown LC889* 8 Unipure Yellow LC182* 1 UnipureWhite LC 981* 1 Phase C Preservative 1 Phase D Parfum 0.1*pigments sold by LCW (France)

All the ingredients of Phase B are mixed and stirred till homogeneity isreached. Phase A is prepared by mixing all its ingredients and heatingto 70° C.; then Phase A is added to Phase B. The mixture of the twophases is homogenised and then cooled down to 40° C.

Phase C and D are added while stirring.

Properties of the foundation:

Viscosity=29500 mPa.s (5 rpm, spindle 4); 48000 mPa.s (2.5 rpm, spindle4); pH=6.9.

Stability.

No separation after 60 minutes of centrifugation at 6000 rpm.

1-15. (canceled)
 16. An inverse emulsion having an aqueous phase and anorganic phase comprising from about 20 to about 70% by weight of anacrylic polymer obtained by the inverse emulsion polymerization of i.from about 55 to 76% by weight of an anionic acrylic monomer containinga strongly acidic functional group; ii. from about 0.1 to 5% by weightof a cationic acrylic monomer of the formula (I):

 wherein R₁ is hydrogen or methyl; R₂, R₃, R₄ are, one independently ofthe others, hydrogen or a C1-C4 alkyl; Y is NH or O; A is a C₁-C₆alkylene; and X is chloride; and iii. from about 25 to 45% by weight ofa C₃-C₅ anionic acrylic monomer containing a carboxylic group; whereinthe weight ratio between the aqueous phase and the organic phase is fromabout 4:1 to about 2:1.
 17. The inverse emulsion according to claim 16,wherein the acrylic polymer is obtained by the inverse emulsionpolymerization of i. from about 60 to 70% by weight of an anionicacrylic monomer containing a strongly acidic functional group; ii. fromabout 2 to 4% by weight of a cationic acrylic monomer of the formula(I); and iii. from about 30 to 40% by weight of a C₃-C₅ anionic acrylicmonomer containing a carboxylic group.
 18. The inverse emulsionaccording to claim 16, wherein the anionic acrylic monomer containing astrongly acidic functional group is 2-acrylamido-2-methylpropanesulfonicacid.
 19. The inverse emulsion according to claim 18, wherein thecationic acrylic monomer of the formula (I) is selected from the groupconsisting of acryloyloxyethyl trimethylammonium chloride andmethacryloyloxyethyl trimethylammonium chloride.
 20. The inverseemulsion according to claim 17, wherein the C₃-C₅ anionic acrylicmonomer containing a carboxylic group is selected from the groupconsisting of acrylic acid and methacrylic acid.
 21. The inverseemulsion according to claim 16, wherein the acrylic polymer obtained byinverse emulsion polymerization is cross-linked with from about 0.01 toabout 1% by weight of a compound containing two or more ethylenicgroups.
 22. The inverse emulsion according to claim 21, wherein theacrylic polymer obtained by inverse emulsion polymerization iscross-linked with methylene-bis-acrylamide.
 23. A procedure for thepreparation of an inverse emulsion comprising: a. preparing acomposition comprising from about 40 to about 60% by weight of water,and for the remaining weight percentage, a mixture of acrylic monomersconsisting of: i. from 55 to 75% by weight of an anionic acrylic monomercontaining a strongly acidic functional group; ii. from 0.1 to 5% byweight of a cationic acrylic monomer of the formula (I)

wherein R₁ is hydrogen or methyl; R₂, R₃, R₄ are, one independently ofthe others, hydrogen or a C₁-C₄ alkyl; Y is NH or 0; A is a C₁-C₆alkylene; X is chloride, iii. from 25 to 45% by weight of a C₃-C₅anionic acrylic monomer containing a carboxylic group; b. adding to thecomposition prepared in a. an aqueous solution of an alkali to regulatethe pH between 4 and 7, a cross-linking agent and an initiator ofradical polymerization, and maintaining the temperature between 3 and 7°C. c. preparing an organic phase containing one or more water-in-oilemulsifiers; d. introducing the mixture obtained in b. into the organicphase prepared in c. and emulsifying the two phases by vigorousstirring; e. initiating the polymerization and completing it maintainingthe temperature between 55 and 95° C. under vigorous stirring; and f.cooling the reaction mixture to 35-45° C. and adding an oil-in-wateremulsifier.
 24. The Procedure for the preparation of an inverse emulsionaccording to claim 23, wherein the mixture of acrylic monomers of thephase a. comprises: i. from 60 to 70% by weight of an anionic acrylicmonomer containing a strongly acidic functional group; ii. from 2 to 4%by weight of a cationic acrylic monomer of the formula I); and iii. from30 to 40% by weight of C₃-C₅ anionic acrylic monomer so containing acarboxylic group.
 25. The procedure for the preparation of an inverseemulsion according to claim 23, wherein the anionic acrylic monomercontaining a strongly acidic functional group is2-acrylamido-2-methylpropanesulfonic acid.
 26. The procedure for thepreparation of an inverse emulsion according to claim 23, wherein thecationic acrylic monomer of the formula (I) is selected from the groupconsisting of acryloyloxyethyl-trimethylammonium chloride andmethacryloyloxyethyl-trimethylammonium chloride.
 27. The procedure forthe preparation of an inverse emulsion according to claim 23, whereinthe C₃-C₅ anionic acrylic monomer containing a carboxylic group isselected from the group consisiting of acrylic acid and methacrylicacid.
 28. The procedure for the preparation of an inverse emulsionaccording to claim 23, wherein the acrylic polymer obtained by inverseemulsion polymerization is cross-linked with from about 0.01 to about 1%by weight of a compound containing two or more ethylenic groups.
 29. Theprocedure for the preparation of an inverse emulsion according to claim28, wherein the acrylic polymer obtained by inverse emulsionpolymerization is cross-linked with methylene-bis-acrylamide.
 30. Aprocedure for preparing a cosmetic comprising preparing the cosmeticusing an inverse emulsion of claim 16.